Chemically Active Particles: From One to Few on the Way to ManyMihail N. Popescu*
Cite this: Langmuir 2020, XXXX, XXX, XXX-XXX
Publication Date:April 1, 2020
ABSTRACT:Chemically active particles suspended in a liquidsolution can achieve self-motility by locally changing the chemicalcomposition of the solution via catalytic reactions at their surfaces.They operate intrinsically out of equilibrium, continuouslyextracting free energy from the environment to power thedissipative self-motility. The effective interactions involving activeparticles are, in general, nonreciprocal and anisotropic, even if theparticles have simple shapes (e.g., Janus spheres). Accordingly, for chemically active particles a very rich behavior of collectivemotion and self-assembly may be expected to emerge, including phenomena such as microphase separation in the form of kineticallystable,finite-sized aggregates. Here, I succinctly review a number of recent experimental studies that demonstrate the self-assemblyof structures, involving chemically active Janus particles, which exhibit various patterns of motion. These examples illustrate conceptssuch as“motors made out of motors”(as suggestively named by Fischer [Fischer, P.Nat. Phys.2018,14, 1072]). The dynamics ofassembly and structure formation observed in these systems can provide benchmark, in-depth testing of the current understanding ofmotion and effective interactions produced by chemical activity. Finally, one notes that these significant achievements are likely justthe beginning of thefield. Recently reported particles endowed with time-dependent chemical activity or switchable reactionmechanisms open the way for exciting developments, such as periodic reshaping of self-assembled structures based on man-madeinternal clocks.